1. Field of the Invention
This invention comprises a method and device for collecting objects pointing out of the bottom level of seas or corresponding water areas so that the objects are conveyed from the seabed by using a collecting device which moves on the bottom of the sea.
2. Description of Related Art
Pieces of mineral, so-called mangan nodules, can be found in the mud at a depth of about 4.5 to 6 km. at the bottom of oceans. The nodules are oval tubers, the minimum diameter of which is approx. 10 to 50 mm. Besides mangan these nodules contain valuable minerals, such as cobolt, nickel and copper. The nodules are to be found on the surface of the mud layers.
Different kinds of equipment have been developed to collect and restore these nodules. The equipment includes a collecting head which moves on the seabed picking up nodules. The nodules are conveyed to a vessel on the surface of the sea by means of hoses by pumping or by using compressed air or by using a hoistable basket. For example U.S. Pat. No. 4,042,279 describes a collecting head solution which uses water flow for collecting nodules.
The problem with the collecting head using water flow is that the intake power needed to remove the nodules is much greater than the power needed to convey the nodules. Large amounts of mud come up with the nodules. Mud has to be separated from the nodules in some way, but the muddy discharge water flow hampers the operation of the equipment located in the collecting head, for example, the echosounder. In addition, mud goes down to the bottom again slowly, which means that the water will be clear only after several days.